1. Field of the Invention
This invention relates to hydraulic hammer and more particularly to self-starting hydraulic hammer.
2. Prior Art
In a typical prior art self-starting hydraulic hammer, the piston and spool, whose valve acts as a switching means for the piston, are each in unspecified free positions during inactive periods. Therefore, application of hydraulic pressure to the hydraulic hammer may not always activate the piston if the piston and spool are not in the proper positional relationship.
In addition, in order to maintain a stable reciprocating motion of the piston, the size and shape of the piston and cylinder used in prior art self-starting hydraulic hammers are limited considerably to very tight tolerances. These tight tolerances limits the freedom of design as well as the capability of the hydraulic hammer. Moreover, since the number of strokes and the speed of the piston is necessiarly determined by the weight of the piston and the applied hydraulic pressure, it is difficult for a proper combination of the number of strokes and energy as a result of various rock conditions, boring diameters, etc. A further disadvantage of the prior art self-starting hydraulic hammers is that the pressing time (the duration during which the piston presses against the boring tool) is too short to deliver an efficient transfer of energy to the rock.